Field of the Invention
The present invention relates to an organic light emitting display device, and more particularly, to an organic light emitting display device that may increase an aperture ratio.
Discussion of the Related Art
Recently, with the development of multimedia, importance of flat panel display devices has been increased. In response to this trend, flat panel display devices such as a liquid crystal display device, a plasma display device and an organic light emitting display device have been commercialized. Of the flat panel display devices, the organic light emitting display device has received much attention as a flat panel display device for next generation, owning to advantages of fast response speed, low power consumption, and excellent viewing angle characteristic based on self-light emission.
FIG. 1 is a circuit diagram illustrating a pixel structure of a general organic light emitting display device.
Referring to FIG. 1, a pixel P of the general organic light emitting display device includes a pixel circuit PC and an organic light emitting device OLED.
The pixel circuit PC includes a switching transistor Tsw, a driving transistor Tdr, and a capacitor Cst.
The switching transistor Tsw is switched in accordance with a scan pulse SP supplied to a scan control line SL, and supplies a data voltage Vdata, which is supplied to a data line DL, to the driving transistor Tdr. The driving transistor Tdr is switched in accordance with the data voltage Vdata supplied from the switching transistor Tsw and controls a data current flowing to the organic light emitting device OLED. The capacitor Cst is connected between gate and source terminals of the driving transistor Tdr, and stores a voltage corresponding to the data voltage Vdata supplied to the gate terminal of the driving transistor Tdr and turns on the driving transistor Tdr at the stored voltage.
The organic light emitting device OLED is electrically connected between a drain terminal and a cathode line EVss of the driving transistor Tdr and emits light through the current flowing in accordance with switching of the driving transistor Tdr.
Each pixel P of the aforementioned general organic light emitting display device controls a size of the data current flowing in the organic light emitting device OLED by using switching of the driving transistor Tdr based on the data voltage Vdata, thereby displaying a predetermined image.
However, in the general organic light emitting display device, a problem occurs in that characteristic (or degradation) deviation of a threshold voltage Vth of the driving transistor Tdr occurs per pixel P due to process deviation caused by non-uniformity of a process of manufacturing a thin film transistor. Also, since degradation speed is varied per driving transistor during long time driving, a defect of picture quality, such as Mura, occurs. As methods for solving the problem caused by characteristic variation of the driving transistor of each pixel, internal compensation technique and external compensation technique are known.
According to the internal compensation technique, a compensation circuit, which includes at least one compensation transistor and at least one compensation capacitor, is added to the pixel circuit PC of each pixel P, and characteristic variation of the driving transistor of the corresponding pixel P is compensated internally through the compensation circuit.
According to the external compensation technique, characteristic variation of the driving transistor of each pixel P is sensed externally by at least a sensing unit of the pixel circuit PC of each pixel P and the sensed result is reflected in data of the corresponding pixel P, whereby characteristic variation of the driving transistor of the corresponding pixel P is compensated through data correction. This external compensation technique is disclosed in the Korean Laid-Open Patent No. 10-2013-0066449 (corresponding to US 2013/0147694).
However, the related art organic light emitting display device to which the internal compensation technique or the external compensation technique is applied has a problem in that an aperture ratio is deteriorated due to the transistor added to each pixel.